U.S. patent number 4,613,543 [Application Number 06/604,710] was granted by the patent office on 1986-09-23 for interpenetrating polymeric network foams comprising crosslinked polyelectrolytes.
This patent grant is currently assigned to Personal Products Company. Invention is credited to Shmuel Dabi.
United States Patent |
4,613,543 |
Dabi |
September 23, 1986 |
Interpenetrating polymeric network foams comprising crosslinked
polyelectrolytes
Abstract
An absorbent body for absorbing body fluids is provided which is
highly liquid retentive and comprises cellular polymeric absorbent
material. The absorbent body of the invention comprises a cellular
interpenetrating polymeric network comprising a crosslinked
polyelectrolyte.
Inventors: |
Dabi; Shmuel (Highland Park,
NJ) |
Assignee: |
Personal Products Company
(Milltown, NJ)
|
Family
ID: |
24420707 |
Appl.
No.: |
06/604,710 |
Filed: |
April 27, 1984 |
Current U.S.
Class: |
428/304.4;
521/134; 521/137; 521/139; 521/86; 525/375 |
Current CPC
Class: |
A61L
15/425 (20130101); A61L 15/60 (20130101); C08G
18/4833 (20130101); Y10T 428/249953 (20150401); C08G
2270/00 (20130101) |
Current International
Class: |
A61L
15/42 (20060101); A61L 15/60 (20060101); A61L
15/16 (20060101); C08G 18/00 (20060101); C08G
18/48 (20060101); B32B 003/26 () |
Field of
Search: |
;428/304.4 ;525/375
;521/137,134,139,86 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
42-22044 |
|
Oct 1967 |
|
JP |
|
56-131616 |
|
Oct 1981 |
|
JP |
|
744027 |
|
Jan 1956 |
|
GB |
|
898272 |
|
Jun 1962 |
|
GB |
|
1137465 |
|
Dec 1968 |
|
GB |
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Sarofim; N.
Attorney, Agent or Firm: Lipow; Jason
Claims
What is claimed is:
1. An absorbent body for absorbing body fluids comprising a
cellular interpenetrating polymer network wherein a first polymer
of said network comprises a foamed polymer and a second polymer of
said network comprises a crosslinked polyelectrolyte.
2. The absorbent body of claim 1 wherein said foamed polymer is
crosslinked to form a full IPN with said crosslinked
polyelectrolyte.
3. The absorbent body of claim 1 wherein said foamed polymer is
linear to form a pseudo IPN with said crosslinked
polyelectrolyte.
4. The absorbent body of claim 1 wherein said foamed polymer is
formed from a foamable polymeric precursor.
5. The absorbent body of claim 4 wherein said foamable polymeric
precursor is selected from the group consisting of
styrene-butadiene, styrene-butadiene acrylonitrile, urethane, epoxy
or acrylic polymers.
6. The absorbent body of claim 1 wherein said foamed polymer is
formed from a foamable reactive oligomer precursor.
7. The absorbent body of claim 6 wherein said foamable reactive
oligomer precursor is selected from the group consisting of
isocyanate terminated polyurethanes, polyesters having unsaturated
carbon-to-carbon bonds, epoxy oligomers, aminoplasts or phenolic
resins.
8. The absorbent body of claim 1 wherein said foamed polymer is
formed from a foamable monomeric precursor.
9. The absorbent body of claim 8 wherein said foamable monomeric
precursor is selected from the group consisting of isocyanate or an
epoxy compound.
10. The absorbent body of claim 1 wherein said crosslinked
polyelectrolyte is formed from a water soluble carboxylic
polyelectrolyte.
11. The absorbent body of claim 10 wherein said water soluble
carboxylic polyelectrolyte is selected from the group consisting of
acrylic acid-acrylate copolymers; acrylic acid-acrylamide
copolymers; acrylic acid-olefin copolymers; polyacrylic acid;
acrylic acid-vinyl aromatic copolymers; acrylic acid-styrene
sulfonic acid copolymers; acrylic acid-vinyl ether copolymers;
acrylic acid vinyl acetate copolymers; acrylic acid-vinyl alcohol
copolymers; copolymers of methacrylic acid with all of the above
monomers; copolymers of maleic acid, fumaric acid and their esters
with all of the above comonomers; copolymers of maleic anhydride
with all of the above comonomers; and the salt forms of all of the
above.
12. An absorbent body for absorbing body fluids comprising a
cellular interpenetrating polymer network wherein a first polymer
of said network comprises a foam polymer and a second polymer of
said network comprises a crosslinked polyelectrolyte and whereas
said first polymer is formed from the group consisting of
(a) foamable polymeric precursors selected from the group
consisting of styrene-butadiene, styrene-butadiene acrylonitrile,
urethane, epoxy or acrylic polymers;
(b) foamable reactive oligomer precursors selected from the group
consisting of isocyanate terminated polyurethanes, polyesters
having unsaturated carbon-to-carbon bonds, epoxy oligomers,
aminoplasts or phenolic resins; or
(c) foamable monomeric precursors selected from the group
consisting of isocyanate or an epoxy resin.
13. The absorbent body of claim 12 wherein said foamed polymer is
crosslinked to form a full IPN with said crosslinked
polyelectrolyte.
14. The absorbent body of claim 12 wherein said foamed polymer is
linear to form a pseudo IPN with said crosslinking
polyelectrolyte.
15. The absorbent body of claim 12 wherein said crosslinked
polyelectrolyte is formed from a water soluble carboxylic
polyelectrolyte.
16. The absorbent body of claim 12 wherein said water soluble
carboxylic polyelectrolyte is selected from the group consisting of
acrylic acid acrylate copolymers; acrylic acid-acrylamide
copolymers; acrylic acid-olefin copolymers; polyacrylic acid;
acrylic acid-vinyl aromatic copolymers; acrylic acid-styrene
sulfonic acid copolymers; acrylic acid-vinyl ether copolymers;
acrylic acid vinyl acetate copolymers; acrylic acid-vinyl alcohol
copolymers; copolymers of methacrylic acid with all of the above
monomers; copolymers of maleic acid, fumaric acid and their esters
with all of the above comonomers; copolymers of maleic anhydride
with all of the above comonomers; and the salt forms of all of the
above.
Description
BACKGROUND OF THE INVENTION
This invention concerns providing cellular polymers suitable for
use in products for absorbing body fluids such as for example,
sanitary napkins, catamenial tampons, diapers, bandages, surgical
dressings and the like. Such materials, commonly referred to as
foams have already been considered for use in such products and in
this connection, polyurethane foams, polyester foams and cellulose
foams have been suggested.
While these foams, in the main, have been capable of absorbing body
fluids to varying degrees, their properties have fallen short of
those preferred for products such as diapers, sanitary napkins and
the like. One such shortcoming is that while these foams may be
formulated to be hydrophilic and hence initially take up large
quantities of aqueous liquids, when subjected to pressure such
liquid is easily expressed, i.e., the fluid retention properties of
these foams are poor. The reason for this is that most of the
liquid held by the foam is mechanically held in the cellular void
spaces and every deformation caused by external pressure tends to
collapse the cell walls, reduce the available void volume and hence
express the liquid. Needless to say, such deforming pressure is to
be expected in absorbent products worn by the user.
It has been suggested that the fluid retention may be improved by
incorporating additional absorbent polymers into the foam. Such
additional polymers, commonly called hydrocolloids or
superabsorbents are water insoluble, swellable, polyelectrolytes
capable of holding many times their weight of liquids and retaining
these liquids under pressure. The insoluble polyelectrolytes are
blended into the foaming mixture as solid particles during the
foaming reaction which forms the foam and hence are distributed in
the finished foam matrix. Such a technique is described in U.K.
Pat. No. 1,550,614. Unfortunately, it has been found that when the
resulting material is wet with body fluids, some of the swollen
gel-like superabsorbent is easily, detached from the foam matrix
thus reducing its efficiency in retaining liquids within the cells
of the foam. Additionally, it has been found that a substantial
portion of the superabsorbent is encapsulated in the polymeric foam
matrix and hence is inhibited from contact with the liquid and
restricted in its abilities to swell and retain liquid.
Accordingly, there is a need for a better way of providing liquid
retentive cellular polymeric absorbent materials.
SUMMARY OF THE INVENTION
In accordance with the teachings of this invention, a cellular
polymeric material, i.e., a foam, is provided for absorbent
products which cellular polymeric material exhibits greatly
improved water retentive properties without the drawbacks
encountered by prior attempts to render such cellular polymeric
material retentive. Specifically, this invention is directed to
providing, as an absorbent body for absorbing body fluids, a
cellular interpenetrating polymeric network comprising a
crosslinked polyelectrolyte.
Interpenetrating polymer networks (IPN's) are already known in the
prior art as exemplified by Sperling, L. H., J. Poly. Sci. Macronol
Rev., 12, 141, (1977); Frisch, H. L., Frisch, K. C., Klempner, D.,
Chemtech, 7, 188, (1977); Lipatov, Yu, S., Sergeva, L. M., Russ,
Chem., Rev, 45, 63, (1976); and Jerome, R., Desreux, V., J. Appl.
Poly. Sci., 15, 199 (1971). They may be defined as polymer mixtures
consisting of two or more polymer networks synthesized within each
other. On the molecular level, they can be viewed as interlocked
molecules of two species which are not chemically bonded to each
other but physically inseparable. Said in other words, polymer
mixtures are often thermodynamically unstable and therefore tend to
phase separate. On the other hand, in the case of IPN's, the
interlocking at the molecular level tends to avoid such
separation.
Different synthesis routes for obtaining IPN's have been described,
the three main ones being:
(1) synthesis of one polymer network, followed by imbibing it with
the monomer of a second polymer, followed by polymerization and
crosslinking, the product being referred to as a sequential
IPN;
(2) mixing two prepolymers of different kinds, followed by
polymerization and crosslinking through an independent mechanism so
as to avoid chemical bonding between the two systems, the product
being referred to as a simultaneous IPN; and
(3) synthesis of one polymer network, followed by imbibing it with
a monomer of a second polymer without a crosslinking agent so that
upon polymerization a linear polymer is obtained which is not
interlocked yet is intimately entangled with the first network, the
product being referred to as a pseudo IPN.
This invention contemplates the formation of all three types of
IPN's wherein at least one of the polymer networks in the system is
a formed i.e., cellular, polymer and the other is a crosslinked
polyelectrolyte. The foamed polymer may be formed from precursors
such as polymers, reactive oligomers, monomers or other components
capable of being roamed into a cellular polymer.
Polymers which may be employed are available in the form of water
based latices such as, for example water latices of
styrene-butadiene, styrene-butadiene acrylonitrile, polyurethane,
epoxy, or acrylic latices.
Reactive oligomers usable are, for example, isocyanate terminated
polyurethanes, polyesters having unsaturated carbon-to-carbon
bonds, epoxy oligomers, aminoplasts (e.g., melamine formaldehyde,
urea formaldehyde), or phenolic resins.
A usable monomer may be, for example, an isocyanate of epoxy
compound.
The polyelectrolates and crosslinking agents combined with the
foamable prepolymers are provided and crosslinked during the
foaming process or after but are not crosslinked prior to the
foaming process. They are chosen such that they will crosslink
through their carboxylic acid functions only and will not react
with the foamable polymer. As a result, a cellular material results
which is a physical blend of interlocked polymers and hence an
IPN.
In a preferred embodiment, a soft, flexible foam is prepared from a
foaming formulation which contains sufficient water to hold in
solution a sufficient quantity of a water soluble polyelectrolyte
and a crosslinker for such polyelectrolyte. Such a system is, for
example, the isocyanate terminated polyether polyols that are
currently suggested for use in a one-to-one weight ratio with water
to produce hydrophilic polyurethane foams. Such a foamable polymer
system is now sold by the W. R. Grace Company under the tradename
Hypol.
DETAILED DESCRIPTION OF THE INVENTION
In the broadest aspects of this invention a cellular
interpenetrating polymeric network comprising a crosslinked
polyelectrolyte is provided for use as an absorbent for absorbing
body fluids. One component of such network comprises a cellular
polymer capable of being formed from such precursors as polymers,
reactive monomers, or oligomers which can be foamed in the presence
of gas. The second component of such a system is a polyelectrolyte,
preferably water soluble, which is capable of being crosslinked
during or after the foaming process to form the interpenetrating
polymeric network with the first component.
The foamed polymer component may be one of many known water
dispersions of polymers or oligomers capable of forming a solid
foamed material in the presence of gas bubbles such as are
introduced by foaming agents or by beating. Examples of such
latices are water dispersions of polyurethane, styrene-butadiene
copolymers, styrenebutadiene acrylonitrile copolymers, epoxy,
acrylic latices including, for example, polymers of ethyl acrylate,
methyl acrylate, methyl methacrylate, buthyacrylate and copolymers
of these. Other synthetic or even natural rubber latices may be
employed.
Additionally, reactive monomers or oligomers capable of
polymerizing and foaming in the presence of gas during the foaming
process are suitable. For example, epoxy terminated oligomers such
as epoxy terminated polyethers, epoxy terminated polyolefin oxides
(e.g., polyethylene oxide, polypropylene oxide and copolymers of
these) which polymerize in the presence of catalysts such as a
tertiary amine of brown trifluoride or polymerize by chain
extention with primary or secondary amines. Unsaturated polyester
oligomers which polymerize in the presence of a catalyst via free
radical polymerization, in combination with a blowing agent, are
also suitable. Additionally, aminoplasts such as melamine
formaldehyde or urea formaldehyde and phenolic resins are usable,
these oligomers being capable of polymerizing in the presence of an
acid catalyst.
The system of choice comprises an isocyanate terminated
polyurethane oligomer which will polymerize and release carbon
dioxide gas during reaction with water and set up to form a solid
polyurethane foam. Such a system is the isocyanate terminated
polyetherpolyols sold by the W. R. Grace Corporation under the
tradename Hypol.
The carboxylic polyelectrolytes component forming the foamed IPN of
this invention are known in the art and are described, for example,
in U.S. Pat. No. 4,310,593 which is incorporated herein by
reference. The essence of usable polyelectrolytes is that they
comprise, at least in the salt form, sufficient carboxylate
moieties to render them soluble in water and hence capable of being
imbibed into the foamed polymer matrix before they are crosslinked.
Usable polymers, capable of being prepared from readily available
monomers and, if necessary for solubilization, capable of being
converted into their salt form, include for example, acrylic
acid-acrylate copolymers; acrylic acid-acrylamide copolymers;
acrylic acid-olefin copolymers; polyacrylic acid; acrylic
acid-vinyl aromatic copolymers; acrylic acid-styrene sulfonic acid
copolymers; acrylic acid-vinyl ether copolymers; acrylic acid vinyl
acetate copolymers; acrylic acid-vinyl alcohol copolymers;
copolymers of methacrylic acid with all of the above monomers;
copolymers of maleic acid, fumaric acid and their esters with all
of the above comonomers; copolymers of maleic anhydride with all of
the above comonomers.
A wide variety of suitable crosslinking agents are usable in
accordance with the teachings of this invention, such crosslinking
agents being, of course, capable of crosslinking the carboxylic
groups of the polyelectrolyte while not reacting to any significant
degree with the foamable precursor matrix to thereby form the IPN
of this invention. Such suitable crosslinking agents are described
in U.S. Pat. No. 4,008,353 and are exemplified by polyhaloalkankols
such as 1,3-dichloroisopropanol, 1,3-dibromoisopropanol; sulfonic
zwitterions such as the tetrahydrothiophene adduct of novolac
resins; haloepoxyalkenes such as epichlorohydrin, epibromohydrin,
2-methyl epichlorohydrin and epiiodohydrin; polyglycidyl ethers
such as glycerine diglycidyl ether, ethylene glycol diglycidyl
ether, propylene glycol diglycidyl ether, diethylene glycol
diglycidyl ether; and mixtures of the foregoing.
A preferred crosslinking agent is that described in my U.S. patent
application Ser. No. 604,709 filed on this day for Crosslinked
Carboxyl Polyelectrolytes and Method of Making Same. Generally
described, such crosslinking agents are low molecular weight, water
soluble compounds having at least two functional groups bonded
thereto which groups have the general formula: ##STR1## wherein the
R groups may be independently selected from the group comprising H,
alkyl having from one to three carbon atoms or alkenyl having from
one to three carbon atoms. The functional groups are preferably
bonded to an aliphatic chain or a substituted aliphatic chain with
the essential criterion that such chains be small enough to insure
that the compound is water soluble. Preferably the compound has a
molecular weight of less than 1000. Such aliphatic or substituted
aliphatic chains may include olefinic groups of from 2 to 12 carbon
atoms; substituted olefinic groups such as olefinic hydroxides,
e.g., butylenehydroxide butylenedihydroxide; mercaptans of olefins
such as mercapobutylene ethers of aliphatic compounds such as
diethylene glycol or triethylene glycol; esters of aliphatic
compounds such as triglycerides or esters of trimethylpropane
pentarithisol.
Several such compounds are already commercially available and it
will be understood by one skilled in the art that a great many
variations of these commercially available compounds can be
synthesized while still conforming to the general description given
above. A particularly effective group of compounds are the
triaziridines based on trimethylolpropane tripropionate adducts
having the formula: ##STR2## and sold by the Aceto Chemical Company
under the trade name TAZ.
Another effective compound, based on pentaerythriol tripropionate
adduct, has the formula: ##STR3## and is sold by Aceto Chemical
Company under the trade name TAZO. Similar materials conforming to
the general description given above are available from Cordoba
Chemical Company under the trade name XAMA. Additionally, other
polyfunctional aziridines that have triazine or phosphate backbones
are also available. Such are, for example,
tris(1-aziridinyl)phosphine oxide, tris(1-aziridinyl)phosphine
sulfide; 2,4,6,trisaziridinyl-s-triazine.
The reaction of the functional group of the aziridine with the
carboxyl group of a carboxylic polyelectrolyte proceeds rapidly at
temperatures of from room temperature or less to about 150.degree.
C. with, of course, increasing reaction rate the highest
temperatures. The reaction proceeds through ring opening as
follows: ##STR4## Crosslinking takes place when a polyfunctional
aziridine molecule reacts as above with carboxyl groups of adjacent
polyelectrolytes to form bridges between these molecules.
The cellular IPN's of this invention are generally synthesized by
first forming a water solution of the polyelectrolyte, the
crosslinking agent and, optionally, a surfactant. Such surfactant
may be included for example, to control the size of the foam cells
or to provide the finished product with enhanced wettability. In
general terms, the ratio of crosslinker to polyelectrolyte should
be, as a minimum, high enough to insure that the polyelectrolyte is
rendered insoluble but not so great as to inhibit the swellability
of the crosslinked product. Usually no more than 30 parts by weight
of crosslinking agent per 100 parts by weight of polyelectrolyte
should be employed and preferably less than 20 parts by weight.
When the crosslinking agent is the preferred polyfunctional
aziridine, the aziridine is dissolved into the solution at a
concentration which may vary from about 0.2 to about 20% by weight,
based on the weight of the carboxylic polyelectrolyte. Preferably,
the concentration should range from 0.5 to 15% and still more
preferably from 1 to 10%. For a given polyelectrolyte, too low a
concentration of aziridine will result in a failure to render the
polyelectrolyte insoluble. On the other hand, too high a
concentration of aziridine will result in a crosslinked product
which exhibits relatively low swelling and hence low absorption
capacity. These properties also vary with the molecular weight of
the uncrosslinked polymer wherein a greater concentration of
crosslinking agent is required to insolubilize a low molecular
weight polyelectrolyte and a lesser quantity of crosslinker may be
employed with higher molecular weight polyelectrolytes. In general,
to obtain best absorption properties, the minimum quality of
crosslinking agent capable of insolubilizing the polyelectrolyte
should be employed.
In accordance with the teachings of this invention, the solution
containing the polyelectrolyte, the crosslinking agent and
optimally the surfactant, is combined with foamable precursor. The
ratio of crosslinked polyelectrolyte to foamable precursor should
be high enough so as to effectively enhance the retentivity of the
foamed polymer. On the other hand, in the case of the preferred
polyurethane oligomer precursors, if too high a ratio is employed
the resulting foamed IPN is stiff, nonresilient and tends to
produce uncontrollably large cells. Generally, the weight percent
of polyelectrolyte based on the weight of foamable precursor should
vary between 3 to 50% with 5 to 20% being preferable.
In producing the foaming mixture, sufficient water must be provided
in the mixture of foamable precursor, polyelectrolyte, crosslinking
agent and surfactant to dissolve the prescribed qualities of
polyelectrolyte and crosslinking agent and still carry out the
foaming process. In the case of employing latices, i.e., water
dispersion sold by various manufacturers, it will be frequently
necessary to add additional water to maintain the remaining
components in solution.
The following examples illustrate the product of this invention,
the method of making the same and the improved properties of the
resulting product.
EXAMPLE 1
A solution of 100 grams of water, 12.5 grams of polyacrylic acid
(obtained from the Rohm & Haas Company and sold by them under
the tradename Acrysol A-5) and 6.5 grams of sodium hydroxide is
prepared. The resulting solution of polysodium acrylate is mixed
with 0.2 grams of the trifunctional aziridine crosslinking agent
obtained from the Aceto Chemical Company and sold by them under the
tradename TAZO. The aqueous solution is combined with 100 grams of
Hypol 4000 urethane prepolymer obtained from W. R. Grace Company
and then is thoroughly mixed by means of a high shear mixer. The
mixture is allowed to foam at room temperature and after one hour,
is placed in a 65.degree. C. air circulating oven for 12 hours to
dry. The resulting foam is soft and has a density of 3.3
lbs/ft.sup.3.
A sample of the dry foam, in the form of a two inch diameter, 3/8
inch thick disk, is weighed and then immersed in a beaker of 1%
NaCl aqueous solution for one hour. The wet foam is suspended in
air for 15 seconds and then reweighed. The foam absorbed 31 grams
of the NaCl solution per gram of foam.
The fluid retention of the foam is determined under both static and
dynamic pressure conditions. For the static pressure test, the disk
sample of the wet foam is rested on a rigid screen. A cast acrylic
cylinder confines the sides of the disk and a piston, weighing 2
killograms is inserted into the cylinder to apply pressure on the
disk. The piston remains on the sample for 15 minutes whereupon no
more fluid is observed as squeezing out of the foam sample through
the screen. The sample is then weighed to determine the fluid
retained. The sample of this example retained 8 grams of NaCl
solution per gram of foam in the static test.
For the dynamic pressure test, higher pressure is applied for a
shorter period of time to evaluate the fluid squeeze out under
sudden pressure. The wet foam sample is placed between two layers
of filter paper and pressure is applied with a 10 lb. roller moving
at a constant speed. The procedure is repeated twice, and the foam
sample is then reweighed to determine the fluid retained. For the
sample of this example, the foam retained 19 grams of NaCl solution
per gram of foam.
EXAMPLE 2
Comparative Example
The procedure of Example 1 is followed with the exception that the
polyacrylic acid polyelectrolyte is omitted. The resulting foam is
soft and has a density of 3.1 lbs/ft.sup.3. The absorption capacity
of the foam is 29 grams of 1% NaCl aqueous solution, about the same
as that of Example 1. The fluid retention of this Example 2 foam,
however, is only 4.7 grams of NaCl solution per gram of foam in
both the static and dynamic pressure tests.
EXAMPLE 3
The procedure of Example 1 is followed, with the exception that one
gram of silicon surfactant obtained from the Union Carbide
Corporation and sold by them under the designation L-562, is added
to the foaming mixture. The resulting foam has similar properties
as those of the Example 1 foam with the exception that larger cells
are formed as a result of the inclusion of the surfactant. This
structure facilitated the fluid transfer within the foam and
increased the absorption rate. It is noted that this wet foam has
about a 75% volume increase caused by the swelling of the
polyelectrolyte polymer.
* * * * *